The goal is to treat spellbooks as properly strategic items. In other words, we don't want players to reserve item slots for them; but traveling back and forth for learning spells isn't ideal either. This is not a huge problem, but I think we can improve the interface nonetheless. Here is the proposal:

Books remain actual items.
You find them on the ground, where you can e.g. set them ablaze under Trog. Identitification rules unchanged.

Treat like runes/gold in inventory.
They don't take up inventory slots, and you can carry as many books as you like (including duplicates).
You access these books through a new command and screen. You can drop them again if you want to (e.g. for proper Trog burning).

New Spellbooks command and screen.
In this screen, you have the following options

Memorise spell.

Forget spell (from a spellbook you carry and choose a spellbook containing it to be destroyed).

Drop book.

Throw book. (I would be willing to remove this option. When I invented book burning, I had dropping in mind.)

The interface of the Spellbooks command needs to be devised carefully: players will amass books, and it can become very hard to navigate through very long lists of spells. Here are some suggestions for this screen:

You can look at spellbooks or the spells within. (Like the Ctrl-F shop interface.)

Sort: by ascending level, by descending leve, or by success.

Toggle schools: In addition you can individually toggle the presence of any spell school. (Currently we have 12 spell schools, so we'd need e.g. keys 1,2,…,9,0,$,&.)
Books without any eligible spells (because you've disabled all their schools) are not listed. Print: “Five books not shown.” or “Showing 5/27 spellbooks” or similar.

We might want special toggles to zoom on or hide artefact books.

The 'M'emorisation command is a shortcut to the spells list of the Spellbooks command, sorted by success and taking care of spells with insufficient slots (greyed out, at the end). All further commands apply (so you can toggle spell schools to narrow down the list).